This invention is directed to a method and apparatus for molding of plastic bottles. More particularly, it is directed to the hot-blow or one-step process for the manufacture of molecularly oriented plastic bottles which is rapid and which has a high degree of component utilization and overall efficiency.
In recent years, substantial effort has been directed to the formation of plastic bottles as a replacement, or partial replacement of glass bottles. This effort has built on knowledge that plastic such as polyethylene terephthalate (PET) when molecularly stretched is tougher but lighter than glass, and the glass art which describes both methods and apparatus for stretching and blowing glass in both the longitudinal and transverse directions.
According to the prior art, molecularly oriented containers such as plastic bottles have utilized primarily either a reheat or two-stage process and system, or a hot-blow or one-stage process and system. In the reheat or two-stage process and system, parisons are first injection molded in a parison mold, cooled to room temperature, and stored for subsequent stretching and blowing into the finished bottle in a blow mold. At the time of stretching and blowing, the parisons are reheated and brought to the orientation and blowing temperature of the plastic prior to blowing. In the hot-blow or one-stage process and system, the parison is injection molded in a parison mold and substantially immediately after formation is transferred while at orientation and blowing temperature to a blow mold where the parison is stretched and blown into the finished bottle.
Of the above-noted systems, the hot-blow or one-stage process and system is preferred. In the reheat or two-stage process and system, although efficient use can be made of both the parison forming and blowing stations which need not be integral, substantial thermal energy is lost during the total operation in that the parison after formation is cooled down and then reheated at time of blowing. Moreover, there is duplicate handling of the parisons. The hot-blow process and system substantially eliminates heat loss and duplicate handling. However, the hot-blow process and system have conventionally employed as an integrated unit an injection assembly, a parison station, a transfer means, and a stretching and blowing station for producing the finished bottle. Generally, the core pin used in forming the parison is transferred with the parison and, accordingly, must serve, at least in part, a double function. Moreover, since the individual components of the system are constructed and arranged as an integral unit, efficient use of the various system components is not realized, nor are the systems as rapid as desired in commercial manufacture.